LCD monitor flickering violently and randomly only after getting "stressed"

[Coconuts 500]

Hello!

I have an LCD monitor from 2009. I can use it for web browsing and similar tasks that do not involve a lot of "activity" on the screen.

But when I try to play a game or watch a movie, it won't take long until the screen starts giving me totally random artifacts. It could be shadowing of the objects on the screen, they could get streched, part of the screen can turn white or black for a split second, etc. But most commonly I get various colors and lines all over the place. It's chaotic. At this point, you can not go back to web browsing or whatever. You have to turn it off and wait for an hour or so.

The fault is not in the computer, as other monitors work fine with it, and I also tried it with my Xbox 360. Same effect.

I've opened it up and checked everything over and nothing looks bad. Solder joints, caps, etc. I tried baking one of the PCBs in the oven (specifically the digital to analog converter board) because it was easy to get out, and because it had a lot of very small solder joints and chips. However, that didn't change anything.

I was going to recap that board too, but gave up because it wasn't possible to unsolder them (even at 450C). I would have to clip them off and solder new caps to the little stumps.

Is this a typical symptom of bad caps in an LCD? I am going to recap it soon regardless, but I would just like to see if anyone has experienced anything like this.

Thank you for your time.

[tom66]

Re: LCD monitor flickering violently and randomly only after getting "stressed"

Would you say it gets worse if the screen has darker content on it, for example if you opened a bitmap editor up and filled the screen with black would it present problems? That sounds like bad caps - LCD monitors draw more current to make black than white (usually) as they are blocking the light which requires the LC to rotate.

[selldoor]

Re: LCD monitor flickering violently and randomly only after getting "stressed"

Hi -welcome to the forum. Please can you update your profile with at least your counry and voltage.
Not sure about baking things - perhaps you know what your doing in that respect?
Melting old solder - it sometimes helps if you introduce some flux and new solder to the pin and if your soldering iron is less then 40w try heating the area beforehand with a hair dryer.

It would be useful if you told us the make and model of the monitor and the part numbers of the boards. Have you used SEARCH above to see of your monitor has featured here before.

We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Example
https://www.badcaps.net/forum/attach...1&d=1290283049

It will be useful if you can say a bit about yourself - skills tools etc.

[Coconuts 500]

Re: LCD monitor flickering violently and randomly only after getting "stressed"

Thank you for your replies.

selldoor- I will provide more info later, I am not at home right now and do not have everything available. But I live in 230V country. It's an LG monitor. That's all I remember.

The black causing problems makes sense. Most recently this happened shortly after I started playing a game. Was walking around and ended up in a dark tunnel. Only a tiny little flashlight as light source, and boom - screen turns crazy.

The power supply has the following caps:

680/25 x2
470/16
470/25 x2
1000/25

1/450
120/450

The D/A board has 4x 100/16 caps.

Mostly Lelon brand caps.

The last board, connected directly to the LCD panel, has no electrolytics.

I will replace all of these shortly. Do I need to use typical "Low ESR" caps, or will general purpose do? I have a lot of caps at home both regular and low ESR, but of course, with my typical luck, none of those values.

Please tell me that the 450V caps are related to the LCD lighting - and that they do not need replacement. The lighting does seem to work right. And I cannot find 450V caps anywhere.

I had an idea. Could bypassing the caps with some 1uf polyester caps potentially improve the problem somewhat? If so, that could be a good way to see if recapping will solve this issue.

More on this later. Thanks again guys.

[selldoor]

Re: LCD monitor flickering violently and randomly only after getting "stressed"

Lelon caps are considered poor if you are buying new and want to give it your best shot
I would go for low esr. Good named make gp would do for some replacements but the difference in price is probably minimal.
The 450v cap is the main power cap - relates to everything but does not usually need replacing unless it shows signs of bulging /leaking.

[Coconuts 500]

Re: LCD monitor flickering violently and randomly only after getting "stressed"

Hi again,

I spoke too soon. I said it works for web browsing, etc, but that is no longer the case. After last night, it is completely unusable. Now all I get are various lines changing about, and sometimes a short flicker of what is supposed to be on the screen.

Why is the cap rated at 450 volts? Are there voltages close to this being used, or is it just a "precaution"?

As for the model of the monitor: LG W43 series. 22".

I now noticed that there's a computer monitor section and this should of course have been posted there. I completely missed that somehow.

EDIT: I am going to order some Panasonic FM caps. Do these have a low enough ESR?

[tom66]

Re: LCD monitor flickering violently and randomly only after getting "stressed"

Hi again,

I spoke too soon. I said it works for web browsing, etc, but that is no longer the case. After last night, it is completely unusable. Now all I get are various lines changing about, and sometimes a short flicker of what is supposed to be on the screen.

If you leave it to warm up, does it start working?

Why is the cap rated at 450 volts? Are there voltages close to this being used, or is it just a "precaution"?

Mains voltage, 230V AC in Europe and other places, is rectified into DC, which produces 325V peak (230V * sqrt(2)). (It's complicated... look up RMS voltage.) Then, because the power company and the EU wants the power you draw from the plug to look as clean as possible, a power factor correction circuit (PFC) boosts it to around 380-420V. So yes, there are high voltages present on the primary side, and you need to be careful.

EDIT: I am going to order some Panasonic FM caps. Do these have a low enough ESR?

Yes, they are very good capacitors. Only FR is better, but there is no need to go above FM.

[Coconuts 500]

Re: LCD monitor flickering violently and randomly only after getting "stressed"

No, it seems to get worse the longer it is on. Basically just becoming a white screen with the occasional thick lines showing up in random places.

The voltage info was interesting. I am aware of peak, RMS voltage and such, but the PFC bit was new to me.

Panasonic FR... I have only seen FRG. Is this the same series? The FRG caps are cheaper (when available), maybe I'll go with those instead.

[tom66]

Re: LCD monitor flickering violently and randomly only after getting "stressed"

No, it seems to get worse the longer it is on. Basically just becoming a white screen with the occasional thick lines showing up in random places.

This could also be a loose LVDS cable, caused by thermal expansion. Did you check this?

The voltage info was interesting. I am aware of peak, RMS voltage and such, but the PFC bit was new to me.

It is a silly requirement when the worst offenders - microwave ovens - have no such requirement, because otherwise the oven would not be £35 but £100+. Similar story for fridges and freezers.

Panasonic FR... I have only seen FRG. Is this the same series? The FRG caps are cheaper (when available), maybe I'll go with those instead.

Hmm. Never heard of FRG. I would stick with FM. They will probably last 20 years in normal use.

[retiredcaps]

Re: LCD monitor flickering violently and randomly only after getting "stressed"

Panasonic FR... I have only seen FRG. Is this the same series? The FRG caps are cheaper (when available), maybe I'll go with those instead.

Panasonic only makes 3 series of low ESR caps available to consumers. They are FC, FM, and FR.

Pansonic FR (only two letters) is the equivalent of FM, but some sizes have better lifetime specs.

[Coconuts 500]

Re: LCD monitor flickering violently and randomly only after getting "stressed"

I'm sorry, I confused the names. The caps I meant were Panasonic NHG. These caps are available in 450V (also, some of them are a little cheaper than FM).

[Th3_uN1Qu3]

Re: LCD monitor flickering violently and randomly only after getting "stressed"

NHG are general purpose. Not suitable for this application. Your issue is likely to be on the logic board, possibly one of the small caps after the 3.3 or 1.8v regulators.